Ouch. There are definitely pitfalls along this path. And if the manager doesn’t understand what the deal implies I’m sure it can be very hard and stressful. Too bad it didn’t work out for your wife.
That’s why it’s good to have two things. One is to be able to easily pick up a job somewhere else for same pay and benefits if required. Second is to say no, ideally in a respectful way. Pretend you have another boss vying for those other 8 hours (this boss is you of course!)